Translation:Year one thousand nine hundred and sixty one
In Swahili or in English?
I can guarantee that the "and" in English is completely correct there; pretty much every dialect outside of America uses "and" in this position. Not everyone speaks American English.
I'm not aware of any mistake in the Swahili either. That na is definitely in the right place.
Not sure this is a U.S. / everybody else English issue. If you're going to go to the trouble of using this date format, the "and" seems to be a natural part of the package.
That said, is this format common anywhere (outside e.g. legislative declarations)? This guy seems not to like it. And even though he writes the "and," he doesn't actually say it, and he's clearly no American.